In conventional casting of nickel or cobalt based superalloy turbine blades, quartz cores are frequently used to produce radial cooling air holes or passages in the castings. Quartz cores are extensively used since quartz is relatively cheap, easily formable into thin cores with bends, and is easy to remove from casting by conventional chemical leaching processes. Furthermore, quartz compared with common core ceramics is considerably stronger and can be formed into more complex shapes without breaking down during the casting. Slender passages as small as 0.003 inch in diameter are now produced in castings through use of quartz tubes, which is used in combination with conventional ceramics to form the core.
Due to these benefits, quartz cores are ideally suited for the manufacture of equiaxed grain turbine blade castings having cast-in holes, where typically range of pouring temperature is from 2550 to 2800 degrees F. Generally at temperatures below 2800 degrees F., unreinforced quartz cores do not distort because of their own weight and also are not deflected by flow of molten metal into the mold.
But occasionally in small blade designs using quartz cores are difficult while injection of them in a wax die has very high risk because of failure of cores due to brittle structure of quartz. Another limitation in the casting of turbine blades with quartz tubes is that the cores are often required to be formed through bending as non linear passage due to the design of the cooling passages in the blade airfoil. Moreover, when the blade has some elements that are close together the design and positioning of cores are very difficult. The cores generally are extended from tip of blade through the root, so that which the cores are extended out from the root and diverged to more than one side, positioning of cores are very considerable because geometry of diverged cores make it difficult, to design of wax injection die.
For positioning the cores in described conditions, the conventional methods such as pins or locators cannot easily be used. Different types of pins and locators are used for solid or tubular cores that have large diameters. These methods cannot be easily applied for cores with small diameters which have bends, especially when they are close together because of several air cooling passages. Other techniques such as wax support used for positioning ceramic solid cores in hollow blades or vanes cannot be used for tubular cores because of their geometry and small diameter.
So an improved method is needed for positioning cores in investment casting process where the multiple cores have the intricate design. An objective of the present invention is to provide a method for positioned cores to meet this need.